This number called and left a really long SILENT message on my voicemail (btw 5-10 minutes). It was just complete silence. No voices. No background noise. So I don't think it was an accidental butt-dial. Because normally, the owner who butt-dialed would be active and moving around, thus making some kind of background noise at a minimal. This was dead silence. Just taking up space in my voicemail and wasted at least 5 minutes (or 10) of my precious time that I could have spent with my children or do something useful.
I forgot to mention that a week after I received the first call from 858-925-2173, I got the same call from a similar number 858-925-2055. Notice that the first 7 digits of both numbers are exactly the same. I believe they are related.